The search for means to harvest energy of ocean currents and tides has a long history and some successes. Several tidal hydropower installation are already in operation for a prolong time. Their wide use is curtailed by the need to use dams or barrages, which besides having high initial construction cost also are damaging environment. Presently there is ongoing search for the means that allow avoiding use of dams and barrages. This means are designed to harvest kinetic energy of water streams instead of potential energy of water elevated by dams or barrages.
There are two major systems for harvesting kinetic energy of water streams—one utilizes propeller type turbines with horizontally oriented axis of rotation the other utilizes Darrieus type turbine, which axis of rotation can be oriented vertically or horizontally. One of the main drawbacks of propeller types turbine is that multiplicator and electric power generators have to be located in waterproof capsule, since axis of propeller rotation is always is underwater. This creates the possibility of this capsule flooding and complicates maintenance service of the generator, multiplicator and related auxiliary systems. One of the advantage of Darrieus type turbine is that in case of vertical orientation of its axis of rotation the multiplicator and electric power generator can be located above water level, thus excluding flooding and simplifying maintenance. The other advantages is that, since Darrieus turbine rotates always in one direction regardless of water stream flow direction, it is better suited for harvesting energy of tide, which frequently changes direction of its flow. The systems utilizing propeller type turbine have to have additional mechanism to entire propeller turbine with multiplicator and electric power generator on 180 degree to accommodate changing direction of tide flow. At the present time it is known about two companies that have projects for harvesting energy of ocean tide and current based on utilization Darrieus type turbine, which was patented in 1927 (U.S. Pat. No. 1,835,018) and was widely used for harvesting kinetic energy of the wind.
One of the two mentioned companies—Blue Energy Canada, Inc. is the pioneer of using Darries turbine for harvesting energy of water streams. Their basic design (see their website www.bluenergy.com) utilizes vertically oriented turbine into a frame that is connected to the sea bottom. This limits their use to shallow water straits and rivers. The other company—GCK Technologies Inc. has systems described in the U.S. Pat. No. 6,036,443, issued to Alexander Gorlov. Specific of this patented turbine is in the use of helical blade instead of conventional straight blade of Darrieus turbine. The goal of using helical blade is to provide to turbine self-starting capability. Presently all 2 and 3 blades Darrieus turbines used for harvesting wind energy and converting it to electricity are started by a motor. Since this motor, after turbine reaches synchronous speed of AC power in the grid, starts to operate as generator the absence of self-starting capability is not a problem at all for systems supplying electricity in power grid.
Installations for harvesting kinetic energy of water streams shown in Gorlov U.S. Pat. No. 6,036,443 are located underwater, thus making them vulnerable for flooding and are not accessible for frequent maintenance. Gorlov also came up with submerged floating system that can anchored in deep waters to sea bottom by mooring lines. This floating system is described in article “Helical Turbines for the Gulf Stream: Conceptual Approach to Design of a Large-Scale Floating Power Farm”, see Marine Technology, Vol. 35, July 1998, pp. 175-182.